Illegal operation appears when opening a Warcraft game program.

I recently installed a game WARCRAFT in my pc. I was able to access the said game for two days now, but lately when I access the game again I encountered an illegal operation warning in my monitor. What will I do?

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If it's not too late do a scanreg /restore back to the days when it worked.
Start in command mode by hitting F8 at boot up, select command mode, enter scanreg /restore and select early date when application worked.

If it can not be restore or restore does take then uninstall, reboot and reinstall.

If still will not open then a virus or hardware problem may exist. That's a longer road.